Rowena is possibly from the Old Germanic hrod ("fame") + wunn ("joy") — or the Old English name Hróðwynn. Lady Rowena of Hengist — semi-legendary 5th-century Saxon princess; her marriage to Vortigern, King of the Britons, is told in Geoffrey of Monmouth's Historia Regum Britanniae (c. 1136); medieval origin legend of Anglo-Saxon England. Rowena King — Trinidadian-British actress (Stargate Atlantis).
Rowena does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Rowena reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.